fix(ui): add py-8 to results state matching document search page

Aligns the top/bottom padding of the Briefwechsel results view with
the document search page wrapper (both py-8).

Refs: #179

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/briefwechsel/+page.svelte

@@ -103,7 +103,7 @@ function selectPerson(id: string) {
 	</div>
 {:else}
 	<!-- Results state: card + content -->
-	<div class="mx-auto max-w-7xl px-4 sm:px-6 lg:px-8">
+	<div class="mx-auto max-w-7xl px-4 py-8 sm:px-6 lg:px-8">
 		<div class="mb-8 rounded-sm border border-line bg-surface p-6 shadow-sm">
 			<CorrespondenzPersonBar
 				bind:senderId={senderId}